Tourniquet occlusion of blood flow is frequently employed during surgery of the arm and leg in humans. At present, however, quantitative information regarding tissue tolerance to tourniquet application is lacking. Therefore, the long-term objective of this research is to determine the maximum time and optimum pressure of tourniquet application. Present knowledge indicates that tourniquet-related injury to muscle and nerve is greatest beneath the tourniquet itself (compared to distal tissues) and that tissues near the tourniquet edge are particularly jeopardized. After tourniquet application to the canine hindlimb for varying times and pressures, newly-developed techniques in our laboratory (labelled pyrophosphate uptake, tissue morphology, noninvasive function apparatus) will be used to evaluate local patterns of tissue injury and long-term myoneural function. These results will be correlated with distribution patterns of tissue pressures (using wick and balloon catheters) and tissue displacement (using radiography and ultrasound) beneath tourniquets applied to isolated muscle specimens, canine hindlimbs, and fresh cadaver limbs. Nerve compression lesions are a significant cause of peripheral neuropathy. Clinically, patients with peripheral nerve compression experience pain, sensory loss, and paralysis. The mechanism by which acute compression affects peripheral nerves is not completely understood. Both ischemic and mechanical factors are implicated as the primary cause of nerve compression lesions. Moreover, the relationship between systemic blood pressure and the tolerance of nerve to increased tissue pressure has not been determined in humans. Recently-developed models of tissue compression in normal human subjects will be employed to determine time-pressure thresholds of nerve dysfunction. Tissue tolerence to external compression will be evaluated in normotensive, hypertensive, and hypotensive subjects by alterations of motor and sensory latencies and amplitudes of affected nerves. During leg compression, the distributions of tissue pressure and tissue displacement will be measured by wick catheters and ultrasonic techniques, respectively. These studies will also help identify the best techniques for neurological examination of the human hand and foot during acute, local nerve compression. Additionally, this research may provide criteria to design a tourniquet which minimizes injury to underlying tissues.